In the related art, there are known observation systems for observing, in 3D culturing in which cells are sterically cultured, the culture state of a cell clump etc. in which a plurality of cells are sterically collected and that has a 3D structure (for example, see PTL 1).
The observation system disclosed in PTL 1 recognizes, in a 2D fluorescence observation image, regions of cell components, such as cell clumps, nuclei, cell membrane, and cell cytoplasm, according to dyes, recognizes and extracts each target site from the 2D fluorescence observation image on the basis of the amount of the dyes, and outputs a measurement value, e.g., the area, of the target site. Furthermore, in order to determine the validity of recognition processing of the target site, the observation system disclosed in PTL 1 confirms both the shape of the target site recognized in the 2D fluorescence observation image and the distribution in a histogram obtained from an analysis result of the target site.